Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$12.63	4.617%	$13.2131	$13.21	$13.20	$13.20
Purchase #2	$166.34	9.792%	$182.628	$182.63	$182.65	$182.60
Purchase #3	$98.77	13.323%	$111.9291	$111.93	$111.95	$111.90
Purchase #4	$248.80	12.619%	$280.1961	$280.20	$280.20	$280.20
Purchase #5	$222.67	11.605%	$248.5109	$248.51	$248.50	$248.50
Purchase #6	$67.43	13.856%	$76.7731	$76.77	$76.75	$76.80
Purchase #7	$136.37	12.302%	$153.1462	$153.15	$153.15	$153.10
7 purchase totals =	$953.01		$1,066.3965	$1,066.40	$1,066.40	$1,066.30